Automatic telephone-exchange system



June 24, 1930.

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ELM/r ATTORNEY Patented June 24, 1930 ras rats

EDGAR I-I. CLARK, orronnsr nr s, nn wennnn w. CARPENTER, or ounnns VILLAGE. NEW Yonx, lasersrons rr-o BELL raterrons nnoaeroains, INCOR- PORATED, or NEW YORK, n. Y., A coaroserron or new reen euro yrerrc 'rnLErnonn-nx HANG}; srsrnar Application filed September 23, 19938. Serial No. 309,176.

This inyention relates to telephone exchange systems andparticularly tothose systems wherein mechanical switching apparatus is employed in the establishment of connections between subscribers lines terminating in manual offices of the exchange area and subscribers lines terminating in machine switching oilices of the same area.

The invention has for its object the simplification of apparatus necessary for the establishment ot such connections and the increased economy in the first cost and maintenance thereof. r

In exchange areas which are being changed through the installation of machine switching apparatus to operate on a full mechanical basis rather than on a strictly manual basis, it is desirable that provision be made for the extension of calls originating in a manual office of the exchange to any of the outlying automatic oihces through the control of the selector switches in the called automatic office by mechanism located at the caling manual ofiice. As the exchange area becomes'mo-re nearly full mechanical through the changing of a greater number of the manual Oli lCGS to automatic oiiices, the need for such control equipment for the remaining manual oihces becomes more essential. By this plan the operator who has answered the call is enabled toestabiish the interofiice connoction which leads to a distant automatic oiiice without assistance,- the entire operation of the switches at the distant automatic otfice being governedby mechanism the originating ofiice controlled by theanswering operator therein.

This has been accomplished satisfactorily the past by circuits of thetype shown, for

et-temple, in Patent 1,513,362,-issued October "328, 19%, to L. M. Allen. present invention was developed to attain the same results as have been heretofore attained in the employment of circuits of the type disclosed-in this patent with simpler apparatus and with greater economy.

iices of the exchange area. Each position is further equipped with a sender controlling keyboard, a set of office keys and or iice code register relays, and a register switch of the step-by-step type which has two functions, first, to controlthe setting oftrunk selecting switches to select a group of trunks to a desired or'iice, corresponding to theoliice code registerd at the position; and second, to registor the number of an idle trunk in the desired otiice group selected by the trunk selecting switches for the purpose of operating indicating lamps at the position to indicate the number of the particular selected trunk.

In order that an idle sender common to all operators positions may be taken for use to extend a call and associated with the operators position concerned, each sender is provided with a step-by-step position finder individual thereto which hunts for a callin operators position. To enable the selected s nder to become associated with an idle tr :nlr outgoing to the desired. automatic ofhce, each sender is associated with a first selector switch individual thereto, which in turn has access either directly or through second selector switches to all of the trunks in the different groups extending to the desired automatic cit-ices.

In the operation of the system the operator who answers an incoming call at the originatin manual office first depresses an ethos key at her-position corresponding to the oflice in which the desired line terminates and thereby causes the position finder switch assoc ated ;-with an idle senderto'huntior her position and to associate it with such sender, and causes the registration of the oflice code designation of the desired line on the office code register relays of her position. She may then depress keys in her key board to register on until the register assumes a position directed by the operated tens code register relay of the position. The first selector then hunts for an idle second selector and the selected second selector and register switch thereafter operate in unison until the register assumes V a position directed by the operated units code register relay. In this manner a group of trunks outgoing to the office in which the desired line terminals is selected. The position register is then restored and is reoperatedin unison with further hunting movements of the second selector until such second selector has selected an idle trunk from a sub-group of trunks in the selected ofiice group. In its reoperated position, the position register causes trunk number indicating lamps at the position to be lighted to indicate to the operator the number of the selected outgoing trunk. The operator then plugs into the jack of the indicated trunk and ier position apparatus is freed for another call. The sender then proceeds to operate the selector switches in the selected automatic ofiice in accordance with the numerical designation registered on the registers thereof in the well known manner. 7

Referring to the drawings Figs. 1 to 10, in-

clusive, arranged in accordance with the diagram of Fig. 12 disclose so much of a telephone system embodying the principles of this invention as is necessary to a comprehensive understanding thereof.

Fig. 1 shows one of a plurality of answering operators positions of a manual ofi'ice provided with cord circuits for extending subscribers"lines over interotfice trunks outgoing to distant dial switching oifices. One of these outgoing trunks terminating in a dial switching oflice is illustrated in this figure.

Fig. 2 shows aset of numerical keys, one ofiice key, a portion of the oflice code registers and control relays of the operators position shown in Fig. 1.

Fig. 3 shows a position finder switch individual to the sender of Figs. 5, 6, 7 and 8 for associating the operators position equipment of Figs. 2 and 4 with such sender.

Fig. 4 shows a trunk number indicating equipment individual to the operators position of Fig. 1 for indicating to the operator the number of the interofiice trunk over which a connection to the desired dial switching otfice is to be extended.

Figs. 5, 6, 7 and 8 taken together show one of a plurality of register senders available for the use of all operators positions of one manual ofiice. Fig. 5 shows two steering switches of the sender. Fig. 6 shows control relays. Fig. 7 shows relay registers for registering the numerical digits of wanted line numbers and Fig. 8 shows counting relays for setting the switches of the dial switching oflice under the control of the registers of Fig. 7.

Fig. 9 shows a first selector individual to the sender and Fig. 10 shows one of a plurality of second selectors for connecting a selected sender with an idle trunk extending to a desired dial switching office.

Fig. 11 shows diagrammatically the arrangement of start circuits for a plurality of position finders, such as the one shown in Fig. 12 is a diagram showing how the various figures should be arranged with relation to each other.

General descmptz'on of apparatus The selector switches 123 and 12 1 diagrammatically illustrated in Fig. 1 and located in the distant dial switching ofiice 122 are of the well known power driven types, such as are shown in the patentto EB. Craft and J. N. Reynolds, No. 1,223,396, granted January 5, 1915. More particularly, they are of the specific type fully disclosed and described in the patent to F. A. Stearn and F. J. Scudder, No. 1,395,977, granted November 1, 1921.

The steering switches 500 and 550 of Fig. 5 are of the rotary single motion step-by-step type driven by stepping magnets from terminal set to terminal set and so arranged that the brushes are moved forward to the next set of terminals upon the deenergization of the corresponding stepping magnet.

The selector switches of Figs. 9 and 10, the position switch 450 of Fig. 4 and the position finder switch of Fig. 3 are of the stepby-step type having both a vertical and a rotary motion. Each switch is provided with a pair of brush sets and corresponding banks of terminals. More specifically, these switches are of the type disclosed in Patent No. 1,700,466, granted to W. W. Carpenter Jan. 29, 1929.

The operators position equipment shown in F ig. 2 comprises a set of ten non-locking digit keys 211 upon which the operator may write up the numerical digits of wanted line numbers, a plurality of oifice keys only one of which 200 has been illustrated and two groups of office code relays, only one relay of each group having been disclosed. As many ofiice keys are provided at each position as ther are dial switching ollices in the exchange are to which the manual oiiice has access. Each such group of code register relays comprises e' ht relays, only the first 01 each group having been disclosed. The register relays of one "roup re istor the tens Detailed description It is believed that the invention will be best understood. from a detailed explanation or the manner in which a connection may be established. To this end it will be assumed that the subscriber of line 100 in the manual ofiice wishes to converse with the subscriber of the line 125 in a distant dial switching oifice 1 2. Upon removing his receiver from the switchhook. the calling subscriber completes a circuit for the energization of line relay 104, which in turn, causes the illumination of lamp .105. The operator upon ObSQIVlB he illumination of lamp 105 answers by ins= ting the plug 102 of one of her cord circuits into the jack 101.v The insertion of the plug in the jack completes a circuit from bat ery through the lamp 107, resistance 106, sleeves of plug 102 and. jack 101, winding of relay .103 to ground. Relay 103 operates and severe the circuit of relay 104 which causes the line lamp 105 to become extin gui sh ed. the switchhook, the insertion of the plug in the jack also completes a circuit from battery through the lower left winding of repeating coil 109, the winding of relay 110, rings of plug 102 and jack 101, over the loop of the line, returning over the tipsot ack 101 and plug 102, upper left winding of repeating coil 109 to ground, Relay 110 operates in this circuit and closes a circuit from battery through its contact, resistances 108 and 106, thence over the path previously trc cod through the winding of relay 103 to ground. This latter circuit shunts the lamp 107 causing the same to remain extinguished. lhe operator next depresses the listening key 112 connecting herheadset into conver .Jsional relation with the calling line and the wishes of the calling subscriber.

Upon learning that he wishes to-talk with r at a distant oilice 22,-the oner- 'ch key corresponds to such distant of- For the purposes of this description,

The receiver being off presses the office key 2000f 2 it will be assumed that the Wanted line numher is CAnal 398-1 and that, therefore, upon the depression of key 200, the No; 2 units code register relay 201 is operated over a circuit extending from battery through the right winding of relay 201, the right contacts or" key 200, right contact of relay 203, the left winding of relay 220 to ground at the left'normal contacts of relay 207, and that the tens code register relay 202 is operated over a circuit from battery through the winding of relay 2.0 1. the left back contact of relay 203, the right Winding of relay 202 to ground at the left contacts of key 200. Relays 201, 202, 20 i and 220 energize in these circuits, relay 220 locking over its right Winding and inner right contact, the inner right back contact of release relay 205 conductor 229 to ground at the back contact of release magnet 100 of the position switch 150. Relays 201 and 202 close a mutual locking circuit for each other extending from battery, through the left winding and left contact of relay 201, the left winding and left contact of relay 202, conductor 231 to ground at the inner let contact of relay 220. Relay 204 operates in the operating circuit of relay 202 and looks through the winding of relay203 the right front contact of relay 204 to ground on conductor 231 and closes a circuit for lamp 232 extending from battery through said lamp, the left contact of relay 204i, conductor 233 to groundat the outer right back contact of relay 401, but relay 203 does notoperate in this locking circuit until the key 200 is released. l1ghts and remains lighted until the trunk number is completely registered on the position switch 450. Upon the release of key 200, relay 203 energizesopening at its back Association of an idlesenoler with the operators position Relay 220, upon ener izing, established a circuit for relay 206 extending from battery through the winding ofsuch relay, the in-' termediate right back contact of relay 207 to ground onconductor231,-a circuit for re- 208 extending from battery, through the Winding thereof, over theouterri-ght back contact of relay 207 to ground OIl COndllCtOl 231 and a circuit for lamp 209 extending from battery through such lamp, the back contact o f-relay 210, the inner right back contact ofrelay 207ito ground on conductor 231. Lamp 209 burns steadily at this time and relay 208, upon energizing, connects the contacts of the keys of keyset 211 to battery through the winding of relay 210. Should the operator prematurely depress a key of the keyset, that is, While the lamp 209 is burning steadily denoting that a sender has not yet been associated with her position equipment, relay 210 will operate looking over its left front contact to ground on conductor 231 and at its right contacts transfers the lamp 209 from steady ground to intermittent ground through the fast interrupter 221. The lamp will thereupon flicker as a signal that the operator should release her position and start the call again. She may do so by depressing the release key 222 thereby operating release relay 205, which in turn releases all operated relays of the position. Relay 208, upon operating, also disassociates the.

key contacts of keyset 211 from conductors 223 to 225, inclusive, extending to the brushes of the position finder of Fig. 3.

Relay 206, upon operating, at its left contact prepares an operating circuit for the cut-off relay 207, extending to conductor 227 and at its right Contact establishes an obvious circuit for the group relay 228. By referring to Fig. 11, it will be noted that provision is made for 100 operators positions, said positions being sub-divided into ten groups of ten positions each. Each subgroup of ten positions has common thereto a group start relay 228. In Fig. 11 the individual startrelays 206 and 206 and cut-off relays 207 and 207 of the first and tenth positions of the first subgroup and the individual start relays'206 and 206 and cut-01f relays 20"? and 207 of the 91st and 100th positions of the tenth subgroup of positions together with corresponding group relays 228 and 228 have been illustrated' A position finder inclividual to a sender such as is shown in Figs. 5 to 8, inclusive, is provided for normally serving each group of ten positions, but the start circuits are so arranged as shown in Fig. 11 that a finder indivdual to any idle sender may be made available to serve any one of the 100 positions.

Referring to Fig. 3 in which the position finder individual to the sender of F igs. 5 to 8 is disclosed for serving the group of positions in which the position of Fig. 2 is located, such finder is illustrated as having a rotary magnet 300, a vertical magnet 301, release magnet 302, off-normal contacts 303 and 32 1, vertical commutator 334 and brush 1 and six shaft brushes 305 to 310, inclusive. Relays 317 and 318' shown in the dotted rectangle are common to all position finders. When therefore the group relay 228 of the subgroup in which the'position equipment of Flg. 2 18 located operates, assuming that the,

finder normally allotted for serving such subgroup 1s idle, a circuit 1s extended from battery, through the winding of relay 311, the make-before-break contacts of relay 312, transfer key 3 14, conductor 313, the left contacts of relay 228, conductor 31% to ground at the left back contact of relay 312. Relay 228 at its outer right contact also connects ground over a conductor, such as 315, to place a calling potential on the commutator of the position finder corresponding to the bank level thereof in which the subgroup of posi tions appear, and at its inner front contact connects ground to conductor 316 for operating the common relay 317. Relay 317 on ergizes in turn operating the common relay 318 in a circuit extending to ground at the back contacts of all relays similar to relay 312 of line finders that are at the time idle. Relay 318, upon operating, furnishes locking battery for the relay of each position finder corresponding to relay 312 for a purpose to be later explained. Relay 311, upon operating, establishes a circuit for relay 319 extending from battery through the left winding thereof, the back contacts of magnets 300 and 301, the front contact of relay 311 to ground at the outer right back contact of relay 331. Relay 319 operates in this circuit and at its leftcontact establishes a circuit for vertical magnet 301 extending from battery through the winding of magnet 301, the back contact of relay 332 to ground at the left contact of relay 319. Magnet 301 energizes, opening the energizing circuit of relay 319. When, therefore, vertical magnet 301 is completely energized and the finder shaft has been advanced vertically one step, relay 319 releases, in turn, opening the operating circuit of magnet 301.

It will be assumed that the calling oper tors position terminates in the first bank level of this finder and that therefore when the finder has been stepped to thislevel, ground potential placed upon commutator terminal 333 by the group relay 228 will be encountered by the commutator brush 30 1 and a circuit completed therefrom over conductor 335, through the left winding of relay'332 to battery through the left winding of relay 319 before the vertical magnet 301 releases. Re-

lays 319 and 332 thereupon energize, relay 319 locking itself energized over its left winding and the back contacts of magnets 300 and 301 upon the release thereof and relay 332 locking itself from battery over its right winding and right contact to ground at the outer right back contact of relay 331. With relays 319and 332 both energized a circuit is now established for the rotary magnet 300 extending from battery through the winding of magnet 300, the left front contact of relay 332 to ground at the left contact of relay 319. Magnet 300 energizes, advancing the brushes of the finder one step in a rotary direction.

The energization of magnet 300 now opens the holding circuit of relay 319 and since its initial energizing circuit was-opened at the commutator brush 304 as soon as the finder rotated one step, relay 319 deenergizes, opening'the operating circuitof magnet 300. This magnet, in turn, deenergizes again closing'an operating circuit for relay 319 extending from battery, through its left winding, back contacts of magnets 300 and 301, the front contact of relay 311 to ground at the outer right back contact of relay 331. Relay 319 again energizes and establishes the operating circuit of magnet 300. In this manner net 300 and relay 31'9'reciprocally o aerate to advance the brushesof the position finder in a rotary hunting movement.

When" the brushes have been so advanced to the terminals associated with the calling operators' equipment, a circuit becomes established from-battery, winding of cut-off relay 207, the left contact of relay 206, conductor 227, test terminal 352, test brush 309, winding of relay 340, rightnormal contacts of relay 331 to ground through the right winding of relay 319, thereby energizing relays 207 and 340 and differentially releasing relay 319. Relay 2'07, upon energizing, looks over its winding and inner left front contact, the outer right back contact of relay 205, directly to conductor 227 independently of relay 206, opens at its right contacts the circuitsof rela s 206 and208, thereby releasing said. relays a-ndat its inner right front contact establishes a' circuit from ground through the slow interrupter 230, over the right backcontact of relay 210 to battery through the lamp 209. Lamp 209 now flashes to indicate that the operators position has been attached to an idle sender andthat she may proceed to operate the keys of keyboard 211 to set the numerical registers of such sender to record the numerical designation of the desired line, The release of relay 206 opens the circuitof group relay 228 which, in turn, releases releasing relays 311, 317 and 318, the two lat-- ter relays releasing. only in case there is no other call initiated at the time.

Relay 340 upon operating closes an obvious circuit over its front contacts for relay 331 which, upon operating, extends control circuits from the operators position equipment over brushes 305 to 308 and 310, inclusive. At its-right back contact relay 331 opens the holding circuit of relay 332, the circuit previously traced through the left winding of relay 319 and at its right make-before-break contacts substitutes direct ground in the circuit of relays 207 and 340 in place of ground through the right winding of relay 319. Relay 332 thereupon, releases. At its interme diate right contact relay331 also closes a circuit extending from ground over such contact, conductor 342, wind-in'g of relay 506,conductor 351 to battery. A circuit is also closed in parallel with relay 506 from ground on conductor 342, through the winding of relay 700 to battery on conductor 351-.

Relay 506, upon energizing, prepares several circuits. At its inner left contact it establishes a circuit for relay 900 of the first selector, extending from ground over conductor 801, winding of relay 800, conductor 902, off-normal contact 901 to battery through the left winding of relay 900. At its inner right contact it establishes a circuitfor relay 600 extending from battery through the right winding of relay 600, conductor 601, the left back contact of relay 505, normal position terminal and brush 503 of steering switch 550, conductor 502 to ground at the inner left contact of relay 506, at its outer right contact it connects holding ground to conductor 509 for locking relays of Figs. 5, 6 and 8 and at its intermediate left contacts establishes a circuit for relay 504 extending from battery through the winding of relay 504, the outer right back Contact of relay 507, the back con tact of relay 565, conductor 508, conductor 606, the inner left back contact of relay 610, conductor 608, the intermediate left front contact of relay 506, the normal position terminal and brush 520 of steering switch 550, conductor 521 to ground at the left back contact of relay 617.

Relay 700, upon energizing at its uppermost front contact, connects ground to conductor 701 for locking the register relays of Fig. 'Z, at its inner upper front contact connects ground over conductor 718, the outer right contact of relay 506 through the winding of relay 506 to battery on conductor 351 for holding itself and relay 506 operated, and at its intermediate lower contact connects ground over conductor 724, the back contact of relay 820, conductor 702, through the winding of release relay 915 of the first selector to battery. Relay 915 energizes in this circuit, at its front contact furnishing locking ground for relay 900 and for other relays of the first selector and at its back contact opening at one point the circuit of release magnet 91?. At its inner lower front contact relay 700 connects ground to conductor 921 for a purpose to be later explained and at its lowermost front contact connects ground over conductor 722 to battery through the left winding of relay 312.

Relay 312 thereupon energizes looking over its left winding and inner leftfront contact and off-normal contact 324 to ground, removes ground at its left back contact from the start conductor 314, removes ground at position finder associated with the idle sendsame subgroup is able to associate another idle sender with such position. For this pur pose it will be assumed that upon the depression of an ofiice key at such other position, for example, the tenth position of such subgroup, relay 206 disclosed in Fig. 11 becomes energized, in turn, operating the common group relay 228. It will further be assumed that the next idle sender is the sender nor mally assigned for serving positions 91 to 100, inclusive. Referring to Fig. 11, with relay 312 energized as just described, a circuit is now established from ground at the lower back contact of relay 312 associated with the position finder individual. to such sender, over the common conductor 314, the lower front contact of group relay 228, conductor 313, transfer key 344, the frontcontact of relay 312, thence in a chain circuit through the front contacts of other relays similar to relay 312 associated with position finders of other busy senders, thence to transfer key 344, the normal contact of relay 312 to battery through the winding of start relay 311". Start relay 311, upon operating, starts the er in the manner previously described. S long as there is an initiated call at any position and any group relay, such as 228, is energized, relay 317 remains energized, in turn, maintaining relay 318 operated until all senders have been taken for use, since relay 318 receives operating ground from common conductor 343, and a back contact of the relay 312 of the position finder associated with each idle sender. With relay 318 energized battery is connected to common conductor 345. Thus, upon the energization of relay 312 an auxiliary locking circuit is established for relay 312 extending from battery on conductor 345, through a winding and inner front contact of relay 312, key 34 the front contact of group relay 228 to ground on common conductor 314. This insures that relay 312 will'be maintained operated if a second call has been initiated in the first subgroup even though the sender which was taken for use by a previously initiated call in that subgroup should become idle. Since relay 312 cannot therefore release to open the chain starting circuit, the second call is not therefore mutilated. e

Relay 504, upon energizing, establishes a circuit for relay 805 extending from battery through the winding of relay 805, conductor 501, the right back contact of relay 510 to ground at the right contact of relay 504. At its outer right contact relay 805 connects ground to conductor 806 for furnishing holding ground for the counting relays, at its inner left contact establishes a circuit for magnet 512 of steering switch 550 preparatory to advancing such switch into position 2, and at its inner right contact establishes a circuit for relay 601. The circuit of magnet Operation of first selector in accordance with first code letter of ofiioe designation It will first be assumed that in order to reach a trunk to the desired office 122 both the first and the second selectors must be used. With relay 601 energized a pulsing circuit for operating the first selector vertically in accordance with the first or tens code letter registered by relay 202 of the operators position is established, extending from battery through the winding of relay 904, back contacts of rotary magnet 905 and vertical magnet 903, inner right back contact of relay 906, intermediate right back contact of relay 907, conductor 908, outer right back contact of relay 809, back contact of counting relay 810, back contact of relay 807, conductor 811, winding of pulsing relay 602, outer right front contact of relay 601, outer right front contact of relay 600, conductor 611, inner right back contact of relay 507, conductor 348, inner right contact of relay 331, brush 310, conductor 235, inner left contact of relay 401, conductor 402, back contact of rotary magnet 403, back contact of Vertical magnet 404, outer left back contact of relay 401, off-normal contacts 430 to ground at the right back Contact of release magnet 400. Relays 602 and 904 energize in this circuit, relay 602 upon energizing closing a circuit for itself over its left contact, rightback con tact of relay 603 to ground at the right back contact of relay 622 independently of ground at the position switch 450 and at its right front contact establishing acircuit for relay 507, extending from battery, winding of relay 507, normal position terminal and brush 516 of steering switch 550, conductor 511, the inner left back contact of relay 605 to ground at the right front contact of relay 602.

Relay 507 at its outer left front contact establishes a circuit for the vertical magnet 404 of the position switch 450, extending from battery through the winding of magnet 404, the outer right back contact of relay 405, the left back contact of release magnet 400, winding of relay 406, the inner right back contact of relay 401, conductor 226, brush 308, inner left contact of relay 331, conductor 320 to ground at the left contact of relay 507. Magnet 404 and slow releasing relay 406 energize in this circuit, magnet 404 stepping the brush shaft of the switch 450 one step i the time energized no circuit exists for relay 504 over the inner left contacts of relay 601. The relay 504 being slow to release does not do so, so long as relay 602 continues to transmit impulses to the winding of relay 507.

lVifh relay 507 energized, it is held energized in a circuit from battery through its winding, left front contact of relay 504, the inner right front contact of relay 507, conductor S48, thence as traced through the left back contact of relay 401 to ground through the back contact of vertical magnet 404 and the left front contact of relay 406. Relay 507 thus does not deenergize until the vertical magnet 404 has fully completed its energization to advance the switch 450 a full step.

Atthe selector of Fig. 9 upon the energization of relay 904 a circuit is closed for the vertical magnet 903 from battery through the winding of magnet 903, the outer right front contact of relay 900 to ground at the inner left front contact of relay 904. Relay 904 also closes an obvious circuitfor relay 909, which disconnects the tip and ring brushes of the selector during its vertical selection movement. Magnet 903 energizes'and at its contacts, opens the previously traced pulsing circuit through the winding of relay 904, and the winding of relay 602. The-selector switch is thus stepped vertically one step,

opening at the off-normal contacts 901 the initial energizing circuit of relay 900.

Upon the opening of the pulsing circuit and the deenergization of relay 602 the-initial energizing circuit of relay 507 is opened and upon the completion of the first step of position switch 450 the holding circuit of relay 507 is opened, whereupon it deenergizes, openingthe operating circuit of magnet 404.

, At the selector upon the deenergization of the vertical magnet 903 following the deenergization of relay 904, the pulsing circuit previously traced is again established, to ground at the front contact of relay 406 and "L relays 602 and 704 again operate both performing the same functionspreviously described to cause the advance of the first'selector and of the position switch 450 another step.

It has been assumed that the first code letter registered upon the tens code register relay 202 was C, having a numerical equivalent of 2. Therefore, when the position switch 450 has advanced two steps vertically and the commutator brush 413 is raised to the second segment of commutator 414-, a circuit will he closed from ground at the outer left contact of relay 220, over the right contact of register relay 202, conductor 236, brush 413, thence over the inner left back contact of relay 401, conductor 285 and as previously traced to battery through the winding of relay 507.

Relay 507 is thus prevented from deenergizing when vertical magnet 404 completes its second energization and therefore the circuit of relay 504 is held open at the outer contact of relay 507 fora sufficient period to permit relay 504 to release. lt'elay'504 upon releasing now opens the circuit of relay 507, which thereupon releases, in turn opening the circuit of vertical magnet .404 and the circuit of slow-to-rclease relay 406. Relay 504 upon deenergizin opens at its rigl'it contact the previously traced circuit for relay 805, which in turn opens the previously traced circuits for relay 601 and magnet 512. hlagnet upon deenergizing advances the steering switch 550-into position 2.

As soon the steering switch leaves normal the previously traced circuit of relay 600 is opened, whereupon a circuit isestablished for relay 505, extending from battery through the winding of relay 505, left back contact of relay 510, conductor 618, outer right back con tact of relay 600, conductor 611, inner right bacl: contact of relay 507, conductor 348, inner right contact of relay 331, brush 310, conductor 235, inner left haclr contact of relay .401, conductor 402, back contacts ofinagnets 403 and 404, outer left hack contact of relay 401 to ground at-the front contact of clay. 406, relay 406 being-slow to release and-having not yetireleased. Relay 505 upon energizing looks over its inner right contact directly to conductor 618 independently of the contacts of relay 510 and closes an obvious circuit for relay 510, which then looks over its inner left contact, conductor 612,the inner right back contact of relay 600 toiground on conduc or 509. Vfith the steering switch in position 2 hrough a circuit is established from battery t the winding of relay 603, the second position terminal and brush 503 of ste ring switch 550, conductor 502 to ground at the inner right contact of-relay 506.

As soon as relay 406 releases following the opening of its circuit; by the dcenergization of relay 507, a circuit is established for relay 405, extending from .battery'through the winding and right normal contacts thereof,

vertical off-normal contacts 415 to ground at the back contactof relay 406. Relay 405 upon energizing locks over its inner right front contact to ground at the right back contact of -release magnet 400 and at its outer right contacts substitutes the winding of the rotary magnet'403 for the winding of the vertical magnet 404 inthe previously traced pulsing circuitextending to the left front contact ofrelay507. Relay 40.6 upon releasing also opens the loc.:ing circui of relay 505 whicl'i then releases. A circuit is nowclosed for relay 556 extending from battery winding of relay 556, right back contact of relay 505, left front contact of relay 510, outer right back contact of relay 600, conductor 611 thence as traced over the outer left back contact of relay 401, the left contact of relay 405 to ground at the back contact of relay 416.

First selector htmts for idle second selector lVhen relay 805 deenergizes, a circuit is established for relay 609, extending from battery through both windings thereof, the outer left back contact of relay 610, conductor 815, the outer left back contact of relay 805, conductor 812, the outer left back contact of relay 622, conductor 619, the inner right back contact of relay 809, conductor 910, the outer right back contact of relay 907, the outer right back contact of relay 906, the inner right front contact and right winding of relay 900, which is wound differentially to the left winding thereof, commutator brush 911 to ground on terminal 912 of the commutator corresponding to the second level of the banks of the first selector, which level of terminals has been assumed to be connected to terminals of trunks extending to second selectors such as the one shown in Fig. 10. Relay 609 operates in this circuit and closes a circuit for relay 614, extending from battery, winding of relay 614, front contact of relay 609 to ground, on conductor 509. Relay 614 upon energizing shunts at its right contact the left winding of relay 609, thereby increasing the current flowing through the right winding of relay 900, whereupon relay 900 differentially releases, removing the vertical magnet 903 from the control of the pulsing relay 904. Relay 900 also connects the right winding of relay 609 over the circuit previously traced to the inner right back contact of relay 900, thence to battery through resistance 7 913, over the back contact of rotary magnet 905. Relay 609 thereupon releases and at its front contact opens the previously traced circuit of relay 614. Since relay 614 is slow to release, a circuit is momentarily closed upon the release of relay 609, from ground on conductor 509, over the back contact of relay 609, the left front contact of relay 614 to battery through the winding of relay 610, which thereupon energizes and locks to ground at the inner left contact of relay 603.

Relay 610 upon energizing opens the initial circuit of relay 609 at its left back contact and at its outer right front contact closes a circuit for relay 615, extending from ground therethrough over right back contact of relay 640, the outer left front contact of relay 610, conductor 815, the back contact of relay 805, conductor 812, thence as traced to battery through resistance 913 at the first selector. Relay 615 operates, in turn operating relay 616 over a circuit extending from battery through the winding of relay 616, outer left back contact of relay 605 to ground at the contact of relay 615. Relay 616 upon operating locks over its right contact to ground at the back contact of pulsing relay 602 and at its left contact establishes an obvious circuit for relay 617, which relay in turn establishes a circuit for magnet 512 of the steering switch 550, extending from battery through the magnet 512 over conductor 513, the outer left back contact of relay 620 to ground at theleft front contact of relay 617 Relay 617 also at its front contact closes a circuit for relay 605, extending from battery through the winding of relay 605, the right front contact of relay 617 to ground at the intermediate left back contact of relay 622.

A circuit is now established for the stepping relay 904 of the first selector extending from battery through the winding of relay 904, back contacts of rotary magnet 905 and vertical magnet 903, back cont-acts of relays 906 and 907, conductor 908, outer right back contact of relay 809, back contact of counting relay 810, right back contact of relay 807, conductor 811, winding of pulsing relay 602, outer right. back contact of relay 601, outer left front contact of relay 603,

outer right front contact of relay 610, right contact of relay 605, conductor 621, second position terminal and brush 514 of steering switch 550, conductor 515 to ground at the intermediate left back contact of relay 622. Relay 904 upon energizing closes the circuit of relay 909 to disconnect the tip and ring brushes of the selector during its rotary hunting movement and closes the circuit of rotary magnet 905, which may be traced from battery through the winding of magnet 905, the outer right back contact of relay 900 to ground at the inner left contact of relay 904. Magnet 905 upon energizing in turn opens the previously traced circuit for relays 904 and 602, relay 904 in turn opening the circuit of magnet 905. Thus, relay 904 and magnet 905 cooperate with each other to cause the step-by-step rotation of the first selector brushes over the selected second level of their banks in search of an idle second selector.

At the sender upon the energization of pulsing relay 602 the holding circuit of relay 616 is opened at the back contact of re lay 602 and relay 616 deenergizes, in turn opening the initial energizing circuit of relay 617. Relay 617 being slow to release, however, does not release before a holding circuit is established therefor from battery through its winding, the inner left frontcontact of relay 605 to ground at the front contact of relay 602. Therefore, as long as relay 602 continues to receive impulses of current due to the hunting movement of the first selector, relay, 617 is held energized and in turn maintains relay 605 operated. Relay 615, at this time deenergizes since its operating circuit was opened'at the back'contact of rotary magnet 905 upon the first energization of magnet 905 and the initial operating circuit of relay 616 is therefore opened at the contact of relay 615.

When an idle second selector is'found, a circuit is established for relay 1015, extending from battery, winding of relay 1015, conductor 918, terminal 919, brush 920, next to inner back contact of relay 909, conductor 921 to ground at the inner lower contact of relay 700. Relay 1015 energizes, connecting locking ground for the relays of thQSGCOIld selector and opening at one point the circuit of release magnet 1017. Another circuitis also established from battery throughthe left winding of relay 1000, off-normal contacts 1001, conductor 1002, terminal 922, brush 914, the outer left back contact of relay 906, the back contact of release magnet 917, inner right back contact and right Winding of relay 907, conductor 902, winding of relay 800, conductor 801 to ground at the inner. left contact of relay 506. Relays 1000 and 907 operate in "this circuit, but due 'to its small number of turns relay 800 does not operate. Relay 1000 upon operating looks over its left contact to ground at the front contact of relay 1015 and at its outer right front contact prepares the operating circuit of the vertical magnet 1003. Relay 907 upon operating locks over its left front'contact to ground at the front contact of relay 915, at its left back contact opens the energizing circuit for relay 906 and at its inner right back contact opens its own initial energizing circuit, and connects the trunk conductors 908 and 910 over its outer and intermediate right front contacts, right back contacts of relay 909, ring and tip brushes 925 and 924 to the selected trunk conductors 1008 and 1010. At its inner right front contact relay 907 connects ground on conductor 902 over the back contact of release magnet 917, the outer left back contact of relay 906, brush 914, terminal 922 to conductor 1002. At its intermediate right back contact relay 907 also opens the circuit previously traced through the windings of relays 904 and-602, whereupon these relays are released. I

- Pulsing relay 602 upon-releasing opens the holdingcircuit of slow-to-release relay 617, which in turn releases relay 605. Relay617 upon releasing also opensthe circuit of magnet 512 which advances the brushes of steering switch 550 into'contact with theirthird position terminals; ,As soon as the steering switch leaves position 2, thecircuit of rel ay 603 is opened and that relay releases, opening the holding circuit ofrelay 610, which also releases in turn releasing relay 615. WVith the steering switch 550 in position3,

the previously traced circuit for relay 504 is again established. With relay 556 energized a circuit is closed for relay 600 extending from battery through the left winding of relay 600, the inner right front contact of relay 556, the third position terminal and brush 503 of steering switch 550 to ground on conductor 502. Relay 600 upon energizing at its inner left contact locks directly over the ,third positionterminal and brush 503 of switch 550 and at itsinner right back contact opens the holding circuit of relay 510 which thereupon releases, in turn releasing relay 556. Relay 510 upon releasing again closes the previously tracedcircuit for relay 805 which in turn closes the previously traced circuits for relay 601 and stepping magnet 512.

Setting the'seoond selector in accordance with second Ofiioe code letter It hasbeen assumed that the second code letter registered on the units code register units relay 201 has established a connection to the terminal of bank 417 of. the position switch 450 in such a manner as to stop the position switch after it has rotated in synchronism with, the vertical stepping of the second selector to measure two vertical steps of such selector. With the steering switch 550 in position 3 a pulsingcir'cuit may now be traced from battery, winding of relay 1004, back contacts of rotary magnet 1005 and vertical magnet 1003, inner right back contact of relay 1006, intermediate right back contact of relay'1007, conductor 1008, brush 925, next to outer rightjback contact of relay 909, intermediate right frontcontact of relay 907, conductor 908, outer right back contact efrrelay 809, back contact ofrelay 810, back contactof relay 807, conductor 811, winding of pulsing relay602, outerright front contact of'relay 601, outer right front contact of relay 600, conductor 611, inner right back contact of relay 507-, conductor 348," inner right-contact ofrelay 331, brush 310, conductor 235, inner left back contact of relay 401, conductor 402, back contact of rotary magnet 403, back contact of vertical magnet 404, outer left back contact of relay401, left contact of relay 405 to ground'at the, back contact of relay 416. Relays 6.02. and 904 energize "in this circuit. Relay 602 upon energizing closes a circuit for itself o'ver'its left contact, the right back cont-actof relay 603 to ground at the right hackcontact of relay 622, independently of ground at the back contact of relay 41 6 a'nd'at itsright front contact, establishes a circuit for relay 507, extending from battery, winding ofrelay 507, third position'terminal and brush 516 to steering switch 550, conductor 5 11,'the I; 

